Patient safety in hysterectomy and myomectomy is important given the large number of women undergoing these procedures (over 600,000 hysterectomies/myomectomies each year). Increasing use of laparoscopic hysterectomy/myomectomy has improved patient outcomes because of lower complication rates and more rapid recovery compared to traditional abdominal surgery. Uterine power morcellation is a technique of tissue removal that enables completion of these procedures with small incisions. However, recent concern about possible spread of occult (i.e., preoperatively undetected) uterine cancer into the peritoneal cavity caused the Food and Drug Administration (FDA) issuing a safety warning in 2014 against the use of power morcellation in hysterectomy/myomectomy. This act has been controversial due to inconclusive data on the risk of occult uterine cancer (expected to be quite low) and the impact of power morcellation on cancer prognosis. Despite sparse data, the highly publicized FDA warning has prompted major changes in clinical practice leading to alterations in surgical routes and techniques. While these changes can reduce the risk of disseminating cancer cells, they may expose patients to higher risk of complications associated with more invasive surgical routes or unknown risks from novice, understudied techniques, posing an urgent patient safety issue. As conventional ways of gathering safety data (e.g., establishment of patient registries) cannot meet the need for timely evidence, the objective of this study is to demonstrate how we can capitalize on existing, large health care databases to provide opportune evidence to inform policy and clinical decisions regarding uterine power morcellation. We have three specific aims: 1) to determine the prevalence and characteristics of occult uterine cancer (uterine sarcoma and endometrial carcinoma) in women undergoing hysterectomy or myomectomy for presumed benign indications; 2) to examine the impact of uncontained power morcellation on cancer prognosis among women with occult uterine malignancy; and 3) to assess practice changes in hysterectomy and myomectomy following the FDA warning, factors that influence practice response, and the associated impact on patient safety and health care costs. Using linked cancer registry and hospital discharge record data from the State of New York and two national databases, this study will provide population-based estimates on the prevalence and prognosis of occult uterine cancer, assess safety and financial impact of the FDA action, and identify patient- and hospital-level factors that may influence practice response. The project is innovative as we use unique existing databases to provide timely evidence to inform policy discussion; we thoroughly evaluate two types of uterine cancer and analyze both inpatient and outpatient hysterectomy/myomectomy to ensure a comprehensive assessment; and we use actual practices observed before and after the FDA warning to simulate real world impact of practice changes. The findings will enhance our ability to deliver evidence-based medicine, and appropriately counsel patients about the risks and benefits of uterine power morcellation.